MAXIMUM POWER POINT TRACKER FOR SOLAR CHARGE CONTROLLER APPLICATIONS

Transcription

1 MAXIMUM POWER POINT TRACKER FOR SOLAR CHARGE CONTROLLER APPLICATIONS PRJ. NO. 64 STUDENT: GITONGA M. JAMES REG. NO. F17/2123/2004 SUPERVISOR: MR. C. OMBURA EXAMINER: MR. DHARMADHIKARY 2009

2 OUTLINE PROJECT OBJECTIVES INTRODUCTION METHODOLOGY PROCEDURE RESULTS DISCUSSION CONCLUSION QUESTIONS

3 PROJECT OBJECTIVES To design a High efficient Maximum Power Point Tracker To Implement the design Test the working of the Design

4 INTRODUCTION Solar energy is a clean, free and renewable natural resource offering environmental friendly source of electricity. Conversion from solar to electrical energy is achieved by photovoltaic (PV) arrays. Since PV arrays are relatively expensive, it is desired to extract maximum power from them at any given time.

5 Introduction (cont.) Maximum Power Point Tracking (MPPT): Technique used in power electronics systems to obtain the maximum possible energy from energy such as solar, wind and tidal.. Its use is desired to compensate for the effect of temperature, ageing, variations in solar radiation (insolation), and load condition in a PV system. Implemented using simple and analog method - Ripple Correlation Control and Fixed reference voltage Method.

6 METHODOLOGY To achieve the MPPT: Characterization of solar panels. Development of a mathematical relation to control the output Voltage of a buck converter. System modelling using Multisim 10.0 and Proteous 7.0 Professional. Practical implementation of the system.

7 Methodology (cont.) Block diagram of the MPPT system: Solar Panels Buck Converter Battery Sensors (V & I) Control Law PWM

8 PROCEDURE Voltage-Current characterization of PV array:

9 Buck converter A step down DC to DC converter. Procedure cont. + Vin - Buck Converter + Vout - Duty Cycle = V out = V in Vout Vin t on t on + t off

10 Procedure cont. Circuitry Implementation of a buck Converter C = L =

11 Procedure Cont.. Tabulation of Array voltage and subsequent Duty cycle and control voltage required for Fixed reference voltage law derivation PV array Voltage Required Control Required Duty Cycle Voltage

12 Procedure Cont Control law relates Control Voltage Panel Voltage Obtained using a linear approximation Required Control voltage Versus PV. Voltage Control Voltage(Vc) Ideal Linearized PV Voltage (Vpv) Linearized equation Vc = Vpv

13 Procedure Cont Fixed reference voltage law derivation Circuit implementation V =15V

14 Procedure Cont Photovoltaic Array characterization For ripple Correlation Control law derivation Photovoltaic Array Characteristics Array Voltage Array Current(mA) Power(mW)

15 Procedure Cont Control law relating sign of differential of Voltage (dv/dt) to sign of product of differential of power and voltage (dp/dt) (Utilizing non-linear dynamics of a Switch mode dc converter to derive RCC law dp/dt =0 Array Power dp/dt > 0 dp/dt < 0 (mw) Sgn Array Voltage (V)

16 Ripple correlation Control method (dv/dt) Procedure Cont circuitry implementation dp/dt

17 Procedure Cont Ripple correlation Control Conditions Comparator Output XOR output Switch Condition Effects Vpv dv/dt Xp Xv S V > 0 > Opens Increases on V Opens Increases V Closes Decreases V closes Decreases

18 Procedure (cont.) Important Sections in the control unit (MPPT): Current sensor: I to V Converter Voltage sensor Control circuit - circuit implementation of the control law Pulse Width Modulator (PWM)- adjusts the duty cycle Square wave generator Sawtooth Wave Generator

19 RESULTS Panel Voltage (Vpv) V Observed Duty Cycle Theoretical Duty Cycle Tracking Error % % % % Average tracking efficiency = ( )/4 = 96%

20 Results cont.. Comparison of theoretical and Practical results Duty Cycle Practical Theoritical Panel Voltage Average tracking efficiency =96%

21 DISCUSSION Maximum power points obtained using the control law were very close to theoretical values. Results obtained from the tests were as expected. The designed MPPT is not dependent on the converter used, making it flexible and adaptable to other dc-dc switching topologies. Divergence occurred for higher values of insolation and Low insolation levels.

22 CONCLUSIONS System is able to track maximum power at different insolation levels. Variations between theoretical and experimental data is due to: Linear approximation of duty cycle Validation of the control laws through a simple and analog MPPT.

23 RECOMMENDATIONS Implementation of the designed MPPT using Microcontrollers Research on integrating the MPPT discussed in this paper with Wind power Research on ways of integrating the designed MPPT to dynamic systems such as solar powered vehicles.

24 Prototype of the Designed Maximum Power Point Tracker

25 Questions

26 Testing of the designed MPPT

27 Square Wave generator

28 Effects of Temperature on Power

29 Solar panel equivalent circuit

30 Block of Fixed Reference Voltage Method

31 -Vpv Current Sensor

32 Analog Multiplier

33 Fixed reference Voltage Circuitry

34 Voltage Sensor

35 Differentiator

36 Complete Circuit Diagram

37 Observed waveform Vpv =18 volts, duty cycle =0.75 (theoretical 0.78)

38 Sawtooth waveform